Sensitivity-settable image capture apparatus

ABSTRACT

An image capture device includes an image pickup unit including a plurality of pixels and photoelectrically converting an object image by the plurality of pixels; a white balance control unit for performing a white balance correction processing on pixel signals from the image pickup unit; and a sensitivity changing unit for changing the sensitivity of photographing, wherein the white balance control unit performs the white balance correction processing such that, as the sensitivity increases, a response to the light source is suppressed.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of application Ser. No. 11/954,703,filed Dec. 12, 2007, the entire disclosure of which is herebyincorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to white balance control techniques at thehigh sensitive image capture by an image capture apparatus such as adigital camera, a digital video camera and the like.

2. Description of the Related Art

Heretofore, in general, in the image capture apparatus such as a digitalcamera, a digital video camera and the like, to adjust color balance forlight sources of different color temperatures, the photographed imagesignal is subjected to a white balance processing.

Here, an outline of the conventional white balance processing will bedescribed.

First, the signal outputted from an image pickup device is digitalizedby an A/D converter, and as shown in FIG. 2, is divided into a pluralityof blocks. The signal of each block includes color signals including R(Red), G (Green), and B (Blue), and a color evaluation value of theblock is calculated using the following formula (1), for example,

Cx[i]=R[i]−B[i]/Y[i]×1024

Cy[i]=(R[i]+B[i]−2G[i])/Y[i]×1024  (1)

(provided that Y[i]=R[i]+2G[i]+B[i])

When a color evaluation value (Cx[i], Cy[i]) falls within the whitedetection range set in advance, it is determined that the block iswhite, so that integral values sumR, sumG, sumB of the color pixelsfalling within the white detection range are calculated to calculate awhite balance coefficient in accordance with the following formula (2)(Japanese Patent Application Laid-Open No. 2003-235050).

WBCo _(—) R=sumY×1024/sumR

WBCo _(—) G=sumY×1024/sumG

WBCo _(—) B=sumY×1024/sumB  (2)

(provided that sumY=(sumR+2×sumG+sumB)/4)

Meantime, the digital camera currently available is designed such thatits sensitivity can be changed over among a plurality of types such asISO100, 200, 400, 800, and 1600 to be set. The larger these values are,the higher the sensitivity is, and photographing can be attained with afewer amount of light, so that even when a shutter speed is fast,photographing can be made under an appropriate brightness. Under thecircumstances such as a room and a night scene in which brightness isnot sufficient, the shutter speed becomes automatically slow, but byincreasing the sensitivity, the shutter speed can be increased.

However, as the sensitivity increase, the image ends up including manynoise components, and this often causes an adverse effect of the roughimage. Thus, under the present circumstances, the high sensitivityphotographing enters the relationship of a tradeoff with the image

Here, coming into a question in the white balance correction at the highsensitivity is the case where the sensitivity is relatively high such asISO800, and 1600, and the case where a low color temperature lightsource such as tungsten and a day light light source is used as anobject lighting source. In this case, when the white balance correctiongains are compared, a B GAIN is applied at a higher level. As a result,a blue noise becomes conspicuous, so that the image quality remarkablydeteriorates.

In Japanese Patent Application Laid-Open No. 2003-235050, a colortemperature is estimated from the WB gain determined by the whitebalance calculation, and when the color temperature deviates from thestandard range, a chroma emphasis is provided with a limiter. Accordingto this method, while the white balance can be prevented from becomingunnatural to some extent, no consideration has been given to therelation between the white balance and sensitivity or the noise.

SUMMARY OF THE INVENTION

Consequently, it is an aspect of the invention to attain an appropriatewhite balance processing with reducing a color noise at the time of highsensitivity.

To achieve the aspect, one embodiment of the present invention providesan image capture apparatus, comprising an image pickup unit including aplurality of pixels and outputting pixel signals of one picture byphotoelectrically converting an object image by the plurality of pixels;a sensitivity changing unit for changing the sensitivity ofphotographing; an operation unit for dividing the pixel signals of onepicture into a plurality of blocks and calculating a color evaluationvalue to estimate a color of each of the plurality of blocks; adetermining unit for determining whether the color evaluation value ofeach of the plurality of blocks fall within in the region determined aswhite on a color space; a white balance correction unit for performing awhite balance correction processing on the pixel signals of one pictureon the basis of the determination result of the determining unit; and achanging unit for changing the range of the region determined as whiteon the color space in accordance with the sensitivity.

Another embodiment of the present invention provides an image captureapparatus, comprising an image pickup unit including a plurality ofpixels and photoelectrically converting an object image by the pluralityof pixels; a white balance control unit for performing a white balancecorrection processing on pixel signals from the image pickup unit; and asensitivity changing unit for changing the sensitivity of imaging,wherein the white balance control unit performs the white balancecorrection processing such that, as the sensitivity increases, aresponse to the light source is suppressed.

Another embodiment of the present invention provides a method forcontrolling an image capture apparatus including an image pickup unitincluding a plurality of pixels and outputting the pixel signals of onepicture by photoelectrically converting an object image by the pluralityof pixels; and a sensitivity changing unit for changing the sensitivityof photographing, the method comprising a calculating process fordividing the pixel signals of one picture into a plurality of blocks,and calculating a color evaluation value to estimate the color of eachof the plurality of blocks; a determining process for determiningwhether the color evaluation value of each of the plurality of blocksfalls within the region determined as white on a color space; a whitebalance correction process for performing a white balance correctionprocessing on the image signals of one picture on the basis of thedetermination result in the determining process; and a changing processfor changing the range of the region determined as white on the colorspace in accordance with the sensitivity.

Another embodiment of the present invention provides a method forcontrolling an image capture apparatus including an image pickup unitincluding a plurality of pixels and photoelectrically converting anobject image by the plurality of pixels; and a sensitivity changing unitfor changing the sensitivity of photographing, wherein a white balancecontrol process for performing a white balance correction processing onpixel signals from the imaging unit is provided, and the white balancecontrol process performs a white balance correction processing suchthat, as the sensitivity increases, a response to the light source issuppressed.

Further features of the present invention will become apparent from thefollowing description of the exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing the configuration of an image captureapparatus according to a first embodiment of the present invention.

FIG. 2 is a view showing an example of dividing a picture into aplurality of blocks.

FIG. 3 is a view showing an example of a white determination result.

FIG. 4 is a flowchart showing a WB correction value calculatingprocessing.

FIG. 5 is a view showing a white detection range variable according tosensitivity.

FIG. 6 is a flag showing variableness of the white detection rangeaccording to sensitivity.

FIG. 7 is a flowchart showing the WB correction value calculationprocessing when changing the detection range by sensitivity.

FIG. 8 is a view showing a limiter range made variable according tosensitivity.

FIG. 9 is a flowchart showing the WB correction value calculationprocessing when changing the limiter range according to sensitivity.

DESCRIPTION OF THE EMBODIMENTS

Exemplary embodiments of the present invention will be described indetail below with reference to the accompanying drawings.

First Embodiment

FIG. 1 is a block diagram showing the configuration of an image captureapparatus according to a first embodiment of the present invention.

In FIG. 1, a solid-state image pickup device 101 includes a CCD, a CMOSsensor, or the like, in which a plurality of pixels aretwo-dimensionally arranged to photoelectrically convert an object imageand output pixel signals of one picture. The surface of the solid-stateimage pickup device 101, for example, is covered by a color filterincluding color elements of R (Red), G (Green), and B (Blue), regularlyarrayed as a Bayer array, so that color photographing can be attained.

A CPU 114 calculates a shutter speed and an aperture value so that thewhole image has an appropriate brightness, and at the same time,calculates a driving amount of a focus lens to bring an object image ina focus detection region into focus. The exposure value (shutter speedand aperture value) and the driving amount of the focus lens, which arecalculated by the CPU 114, are sent to a control circuit 113, and basedon each value, the exposure control and the focus control are performed.

A white balance (WB) control unit 103 calculates a WB correction valuebased on the information from the image signal stored in a memory 102,and by using the calculated WB correction value, performs a WBcorrection on the image signal stored in the memory 102. Incidentally, adetailed configuration of this white balance control unit 103 and thecalculation method of the WB correction value will be described later.

A color conversion matrix circuit 104 converts the image signalsubjected to the WB correction by the WB control unit 103 into colordifference signals R-Y and B-Y by applying a color gain so as to bereproduced in an appropriate color.

A low-pass filter (LPF) 105 restricts the bands of the colordifferential signals R-Y and B-Y, and a CSUP (Chroma Suppress) circuit106 suppresses a saturated false color signal included in the imagesignal the band of which is restricted by the LPF circuit 105.

On the other hand, the image signal subjected to the WB correction bythe WB control unit 103 is also outputted to a luminance signal (Y)generating circuit 111, in which a luminance signal Y is generated, andthe generated luminance signal Y is subjected to an edge emphasizingprocessing by an edge emphasizing circuit 112.

The color differential signals R-Y and B-Y outputted from the CSUPcircuit 106 and the luminance signal Y outputted from the edgeemphasizing circuit 112 are converted into RGB signals by a RGBconversion circuit 107, and are subjected to gradation correction in agamma correction circuit 108. After that, the signals are converted intoa YUV signal in a color luminance conversion circuit 109, compressed ina compression circuit 110, and then recorded as an image signal on anexternal memory medium or an internal memory medium.

The image capture apparatus shown in FIG. 1 is provided with asensitivity selector switch (not shown) to change the sensitivity at thetime of photographing. In the present embodiment, the gain for the pixelsignals of one picture from the solid-state image pickup device ischanged according to the switching of the sensitivity selector switch,so that the sensitivity at the time of photographing is changed.

Next, a method for calculating the WB correction value in the WB controlunit 103 will be described by using the flowchart of FIG. 4.

First, the image signal stored in the memory 102 is read out, and thepicture represented by the read-out image signal is divided into theoptional number m of blocks (step S101). For every block i (i=1 to m),the pixel values are averaged to calculate a color average value (R[i],G[i], B[i]) for each color. By using the formula (1), the colorevaluation values (Cx[i], Cy[i]) are calculated (step S102). That is,

Cx[i]=(R[i]−B[i])/Y[i]×1024

Cy[i]=(R[i]+B[i]−2G[i])/Y[i]×1024  (1)

(provided that Y[i]=R[i]+2G[i]+B[i])

Next, it is determined whether the color evaluation value (Cx[i], Cy[i])of the i-th block calculated in step S102 falls within the whitedetection range 301 set in advance in the color space shown in FIG. 3(step S103).

The white detection range 301 plots the color evaluation valuescalculated by photographing in advance the white under different lightsources in advance. The negative direction of an x coordinate (Cx) inFIG. 3 shows a color evaluation value provided when photographing thewhite of a high color temperature object, and the positive directionshows a color evaluation value provided when photographing the white ofa low temperature object. The y coordinate (Cy) indicated a degree ofthe green component of the light source. As the G component progressestoward the negative direction, it becomes large. This means that it is afluorescent lamp.

When the calculated color evaluation values (Cx[i], Cy[i]) fall withinthis white detection range 301, it is determined that that block is awhite color (Yes at step S103), and the color average values (R[i],G[i], B[i]) of that block are integrated (step S104). When the colorevaluation values (Cx[i], Cy[i]) do not fall within the white detectionrange 301, no addition is made, and the procedure advances to step S105.

The processings of steps S103 and S104 can be represented by the formula(3) as follows.

$\begin{matrix}{{{SumR} = {\sum\limits_{i = 0}^{m}{{{Sw}\lbrack i\rbrack} \times {R\lbrack i\rbrack}}}}{{SumG} = {\sum\limits_{i = 0}^{m}{{{Sw}\lbrack i\rbrack} \times {G\lbrack i\rbrack}}}}{{SumB} = {\sum\limits_{i = 0}^{m}{{{Sw}\lbrack i\rbrack} \times {B\lbrack i\rbrack}}}}} & (3)\end{matrix}$

Here, in the formula (3), when the color evaluation values (Cx[i],Cy[i]) fall within the white detection range (301 of FIG. 3), Sw[i] isset to 1, and when do not fall, Sw[i] is set to 0. Based on thissetting, whether the addition of the color evaluation values (R[i],G[i], B[i]) should be performed or not in accordance with thedetermination of step S103 is substantially attained.

At step S105, it is determined whether the above described processinghas been performed on all the blocks i (i=1 to m). If the block notprocessed is still present, the procedure returns to step S102 to repeatthe above described processing. If the processing for all the blocks iscompleted, the procedure advances to step S106.

At step S106, from the integral values (addition values) (sumR, sumG,sumB) of the obtained color evaluation values, the WB correction values(WBcol_R, WBcol_G, WBcol_B) are calculated by using the followingformula (4).

WBCol _(—) R=sumY×1024/sumR

WBCol _(—) G=sumY×1024/sumG

WBCol _(—) B=sumY×1024/sumB  (4)

(provided that sumY=(sumR+2×sumG+sumB)/4)

By using the calculated WB correction values, the white balancecorrection is performed.

Next, a white balance variable response control will be described.

The method thereof is to obtain the sensitivity information at the timeof photographing and make the white detection range variable based onthat information.

Specifically, as shown in FIG. 5, by changing the white detection rangeon the basis of the sensitivity information at the time ofphotographing, the color noise at the time of high sensitivity issuppressed. This change of the white detection range is performed by theWB control unit 103 based on the sensitivity information inputted fromthe CPU 114. FIG. 5 shows a state in which the white detection range inthe low color temperature direction is made variable.

The detection range may be made variable in each of three directions,i.e., the low color temperature side (Cx direction), the high colortemperature side (Cx direction), and the color component direction (Cydirection) which determines a degree of closeness to the color of thefluorescent lamp.

To be more in detail, for example, as shown in FIG. 5, when thesensitivity Sv at the time of photographing is Sv≦Sv1 (low sensitivitytime), it is decided as the white detection range of (a), and whenSv=Sv2 (intermediate sensitivity time), it is decided as the detectionrange of (b), and when Sv≦Sv3, it is decided as the detection range of(c). As shown in FIG. 6, when the sensitivity Sv is Sv1<Sv<Sv2, theranges (a) and (b) are subjected to linear interpolation according tothe sensitivity, and when the sensitivity Sv is Sv2<Sv<Sv3, the ranges(b) and (c) are subjected to linear interpolation according to thesensitivity so as to calculate the white detection range. As for the WBcorrection value calculation processing, as shown in FIG. 7(particularly at step S203), the same processing as the flow shown inFIG. 4 is performed except that the white detection range is madevariable according to the sensitivity.

As the sensitivity increases, the range of the low color temperaturedirection of the white detection range is narrowed, so that the range ofthe R (Red) direction of the white detection range is narrowed, and thiscan prevent the blue noise from becoming conspicuous by applying the B(Blue) gain small.

Second Embodiment

While the first embodiment has made the white detection range variableaccording to the sensitivity, in this second embodiment, as shown inFIG. 8, a limiter range is changed according to the sensitivity, so thatwhen an output of the white detection result is out of the limiterrange, it is clipped to a limit value.

FIG. 8 also shows the case where a low color temperature direction onlyis made variable similarly to the first embodiment. The limiter rangemay be made variable in direction, i.e., a low color temperature side(Cx direction), a high color temperature side (Cx direction), and thecolor component direction (Cy direction) which determines a degree ofthe closeness to the color of a fluorescent lamp.

This operation will be described by using a flowchart of FIG. 9.

Since the same processing as in FIG. 4 is performed up to step S306, thedetailed description thereof will be omitted.

When a white detection result outputted at step S306 is out of thelimiter range, as shown in FIG. 9, it is clipped to the limiter range asshown in FIG. 9, (step S308), and then a final WB correction coefficientis calculated (step S309).

On the other hand, when the white detection result falls within thelimiter range, the final WB correction coefficient is calculated basedon the white detection result outputted at step S306 (step S309).

While, in the first and second embodiments, a unit for changing therange (specifically, white detection range and the limiter range) of theregion determined as white on the color space, in accordance with thesensitivity has been described, another unit may be used.

For example, the range of the region determined as the white on thecolor space is not made variable according to the sensitivity, but thelimiter of the white balance gain may be made variable according to thesensitivity.

That is, at the time of high sensitivity, the range of the regiondetermined as the white on the color space or the limiter of the whitebalance gain may be made variable according to the sensitivity so thatthe white balance processing is performed such that the response to thelight source is suppressed.

Another Embodiment

An object of each embodiment is achieved by the following method. Thatis, the memory medium (or the memory media) which records the programcode of the software to realize the functions of the above describedembodiments is provided to the system or the apparatus. The computer (orCPU or MPU) of the system or the apparatus reads and executes theprogram code stored in the memory medium. In this case, the program codeper se read from the memory medium realizes the function of theembodiments, and the memory medium storing the program code includes thepresent invention. The execution of the program code read by thecomputer realizes not only the functions of the above describedembodiments, but the present invention also includes the following case.That is, based on the instructions of the program code, the operatingsystem (OS) and the like working on the computer performs a part or thewhole of the actual processing, and according to that processing, thefunctions of the above described embodiments are realized.

The following case is also included in the present invention. That is,the program code read from the memory medium is written in the memoryprovided for a function expansion card inserted into the computer or afeature expansion unit connected to the computer. After that, based onthat program code, the CPU and the like provided for the featureexpansion card or the function expansion unit performs a part or thewhole of the actual processing, and by that processing, the functions ofthe above described embodiments are realized.

When the present invention is applied to the memory medium, the memorymedium is stored with the program code corresponding to the proceduresas described above.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2006-346656, filed on Dec. 22, 2006 which is hereby incorporated byreference herein in its entirety.

1. An image capturing apparatus, comprising: an image pickup unitincluding a plurality of pixels and outputting pixel signals of onepicture by photoelectrically converting an object image by the pluralityof pixels; a sensitivity changing unit for changing the sensitivity ofphotographing; an operation unit for dividing the pixel signals of onepicture into a plurality of blocks and calculating a color evaluationvalue to estimate a color of each of the plurality of blocks; adetermining unit for determining whether the color evaluation value ofeach of the plurality of blocks falls within a region determined aswhite on a color space; a white balance correction unit for performing awhite balance correction processing on the pixel signals of one pictureon the basis of the determination result of the determining unit; and achanging unit for changing the range of a region determined as white onthe color space in accordance with the sensitivity, wherein the changingunit changes the range of a region determined as white by applying alimiter to the region determined as white.
 2. A control method of animage capturing apparatus including an image pickup unit including aplurality of pixels and outputting pixel signals of one picture byphotoelectrically converting an object image by the plurality of pixels,comprising the steps of: changing the sensitivity of photographing bythe image pickup unit; dividing the pixel signals of one picture, outputfrom the image pickup unit, into a plurality of blocks and calculating acolor evaluation value to estimate a color of each of the plurality ofblocks; determining whether the color evaluation value of each of theplurality of blocks falls within a region determined as white on a colorspace; performing a white balance correction processing on the pixelsignals of one picture on the basis of the determination result in thedetermining step; and changing the range of a region determined as whiteon the color space in accordance with the sensitivity, wherein thechanging step changes the range of a region determined as white byapplying a limiter to the region determined as white.
 3. Anon-transitory computer-readable storage medium storing a computerprogram comprising a program code for causing a computer to function, ina control method of an image capturing apparatus including an imagepickup unit including a plurality of pixels and outputting pixel signalsof one picture by photoelectrically converting an object image by theplurality of pixels, as: a sensitivity changing unit for changing thesensitivity of photographing; an operation unit for dividing the pixelsignals of one picture into a plurality of blocks and calculating acolor evaluation value to estimate a color of each of the plurality ofblocks; a determining unit for determining whether the color evaluationvalue of each of the plurality of blocks falls within a regiondetermined as white on a color space; a white balance correction unitfor performing a white balance correction processing on the pixelsignals of one picture on the basis of the determination result of thedetermining unit; and a changing unit for changing the range of a regiondetermined as white on the color space in accordance with thesensitivity, wherein the changing unit changes the range of a regiondetermined as white by applying a limiter to the region determined aswhite.